What is parasite species richness?

  • Number of parasite species known to infect a given host

Does consider:

  • the total number
  • phylogenetic relationships (sometimes)
  • functional traits (sometimes)

Does not consider:

  • relative utilization of hosts
  • effects on host fitness

What is parasite host range?

  • Number of host species known to be infected by a given parasite

Does consider:

  • the total number

Does not consider:

  • relative utilization of hosts
  • effects on host fitness
  • etc.

Parasite host range

What are some potential challenges in estimating parasite host range?

Predicting parasite host range

  • What are some approaches to estimating parasite host range?
  • At what scale is host range defined (a country? a species?)

Predicting parasite host range

Dallas et al. 2017 PRSB

Estimating host range

Dallas et al. 2017 PRSB

What determines parasite host range?

  • physical factors (skin thickeness)
  • environmental factors?!
  • host phylogenetics

Host range is just a number

The number of host species a parasite infects. How might this not be a good measure of specificity?

What is host specificity?

  • Broad term related to the diversity of host species a parasite can infect
  • Parasites may be specific in multiple ways
    • number of hosts (host range)
    • tissue tropism
    • morphological specificity

Different measures of specificity

  • taxonomic (basically host range)
  • phylogenetic
  • functional

Dallas et al. 2020 J Animal Ecology

What are the benefits and costs of specializing?

When would specificity be good/bad?

Maybe specificity does not exist?

Canard et al. 2014 American Naturalist

…but it does.



How do we know that it does?

What other ways can we think about specificity?

  • structural specificity

Poulin et al. 2011 Trends in Parasitology

What other ways can we think about specificity?

  • phylogenetic specificity

Poulin et al. 2011 Trends in Parasitology

What other ways can we think about specificity?

  • specificity across space

Dallas & Jordano 2022 Global Ecology and Biogeography

Are there tradeoffs in different specificities?

Poulin et al. 2011 Trends in Parasitology




End of lecture 1

Host range versus parasite species richness

  • Host range is from the parasite’s perspective.

  • Parasite species richness is from the host’s perspective.

What controls parasite species richness?

Dallas et al. 2020 J Animal Ecology

What controls parasite species richness?

  • Body size

  • Geographic range size

  • Host population density

  • Host immune function?

Kamiya et al. 2013 Biological Reviews

A note about parasite diversity



Have we sampled host species well enough to know who infects who?

The global distribution of undiscovered helminth parasites

Carlson et al. 2020 Proceedings B

Predicting host-parasite interactions

  • Why is it important?

  • What are the features of host and parasite that allow for infection?


  • What’s the goal of this?

  • How do we do it?

Let’s brainstorm what information we’d want to have

Sevilleta host-parasite network

Dallas et al. 2017 PLOS computational biology

Potentially important traits

Dallas et al. 2017 PLOS computational biology

What traits came out of model as important?

Dallas et al. 2017 PLOS computational biology

Meaning to host range/parasite species richness?

Dallas et al. 2017 PLOS computational biology

Predicting potentially zoonotic parasites

Albery et al. 2021 Nature microbiology

Using phylogenetic information to predict associations

Farrell et al. 2022 J of Animal Ecology

Using latent network structure to predict associations

Poisot et al. 2023 Patterns

Using latent network structure to predict associations

Poisot et al. 2023 Patterns

What have we learned?

  • What is parasite host range, specificity, and parasite species richness.
  • Different ways to measure parasite specificity
  • How we can predict unknown host-parasite interactions (and what this means for specificity)